Multi-drop ink-jet recording method with compensation for image density non-uniformities

Abstract

After an ink-jet recording head with a plurality of discharging portions arranged is main-scanned in a direction perpendicular to the direction of the discharging portion arrangement to record a first image area, sub-scanning of the head is performed. Before the head is main-scanned to record a second image area, the sub-scanning is performed so that a few discharging portions on an upper edge portion of the head in second main-scanning overlap part of the first image area. Ink droplets land on pixels in the overlapping portion twice for each main-scanning, and image density of the pixels in the overlapping portion is controlled by the sum number of the landing ink droplets. This enables image density unevenness of image density, example, a "black stripe (banding)" or a "white stripe (banding)" in a boundary of an image area being recorded in each main-scanning, to be markedly reduced.

What is claimed is: 
     
       1. An ink-jet recording method, in which a plurality of ink droplets for each pixel are overlapped and landed on a recording medium to form each pixel by a recording head with a plurality of ink discharging portions arranged thereon in a discharging portion arrangement and a tone wedge of an image data is represented by controlling an area of said each pixel on a basis of a number of the plurality of ink droplets, said method comprising the steps of: recording one image area by main-scanning of said recording head and said recording medium relative thereto in a direction other than a direction of said ink discharging portion arrangement;   sub-scanning said recording head and said recording medium relative thereto in a direction perpendicular to the direction of said main-scanning; and   recording a following image area by main-scanning said recording head and said recording medium relative thereto,   wherein said sub-scanning is performed in a manner that part of said one image area overlaps part of said following image area, and a number of ink droplets discharged from at least two ink discharging portions of said plurality of ink discharging portions, which relates to recording of pixels included in an overlapping portion of said one and following image areas, is modified when said one and following image areas are recorded, so that the tone wedge of a recording image of said pixels included in said overlapping portion is represented by a total number of ink droplets being discharged when said one and following image areas are recorded and said number of ink droplets discharged from said at least two discharging portions for recording said overlapping portion, is gradually decreased toward a discharging portion disposed in an edge portion of said recording head when said one image area is recorded, and is gradually increased from a discharging portion disposed in an edge portion of said recording head when said following image area is recorded, so that said total number of discharged ink droplets is obtained.   
     
     
       2. An ink-jet recording method as claimed in claim 1, further comprising the step of adjusting a discharge position of said recording head relative to said recording medium for each recording step so that each pixel included in said overlapping portion is formed by partially overlapping one image portion being formed by a group of ink droplets discharged when said one image area is recorded with a following image portion being formed by a group of ink droplets discharged when said following image area is recorded, by less than a pixel pitch. 
     
     
       3. An ink-jet recording method as claimed in claim 2, wherein said adjusting step comprises adjusting an amount of sub-scanning. 
     
     
       4. An ink-jet recording method as claimed in claim 2, wherein said adjusting step comprises adjusting a record starting position of said main-scanning. 
     
     
       5. An ink-jet recording method as claimed in claim 1, wherein said total number of ink droplets is a number of ink droplets determined to obtain a predetermined tone wedge of the recording image of pixels when said pixels are formed without overlapping thereof. 
     
     
       6. An ink-jet recording method as claimed in claim 1, wherein said recording head comprises heating elements each of which produces thermal energy for discharging ink in response to an electric current. 
     
     
       7. An ink-jet recording method, in which a plurality of ink droplets for each pixel are overlapped and landed on a recording medium to form each pixel by a recording head with a plurality of ink discharging portions arranged thereon in an ink discharging portion arrangement and a tone wedge of image data is represented by controlling an area of said each pixel on a basis of a number of the plurality of ink droplets, said method comprising the steps of: recording a one image area by main-scanning of said recording head and said recording medium relative thereto in a direction other than a direction of said ink discharging portion arrangement;   sub-scanning said recording head and said recording medium relative thereto in a direction different from the direction of said main-scanning, by a length less than a width of said one image area; and   recording a following image area by main-scanning said recording head and said recording medium relative thereto, whereby said one and following image areas are partially overlapped with each other,   wherein a number of discharging portions for recording pixels included in an overlapping portion of said one and following image areas is two or more, a number of ink droplets being discharged from said two or more discharging portions for recording said overlapping portion, is gradually decreased toward a discharging portion disposed in an edge portion of said recording head when said one image area is recorded, and is gradually increased from said discharging portion disposed in said edge portion of said recording head when said following image area is recorded, so that a total number of discharged ink droplets, being discharged when said one and following image areas are recorded is obtained.   
     
     
       8. An ink-jet recording method as claimed in claim 7, wherein said recording head comprises heating elements each of which produces thermal energy for discharging ink in response to an electric current. 
     
     
       9. An ink-jet recording method, in which at least one ink droplet for each pixel is landed on a recording medium to form each pixel by a recording head with a plurality of ink discharging portions arranged thereon in an ink discharging portion arrangement and a tone wedge of an image data is represented by controlling an area of said each pixel on a basis of a quantity of ink based on density data, said method comprising the steps of: recording one image area by main-scanning of said recording head and said recording medium relative thereto in a direction other than a direction of said ink discharging portion arrangement;   sub-scanning said recording head and said recording medium relative thereto in a direction perpendicular to a direction of said main-scanning; and   recording a following image area by main-scanning said recording head and said recording medium relative thereto,   wherein said sub-scanning is performed in a manner that part of said one image area overlaps part of said following image area and said density data corresponding to at least two discharging portions of said plurality of discharging portions, which relates to recording of pixels included in an overlapping portion of said one and following image areas, is modified when said one and following image areas are recorded, so that the tone wedge of a recording image of said pixels included in said overlapping portion is represented by a total of the quantity of ink discharged when said one and following image areas are recorded and said density data corresponding to said at least two discharging portions for recording said overlapping portion, is gradually decreased toward a discharging portion disposed in an edge portion of said recording head when said one image area is recorded, and is gradually increased from said discharging portion disposed in said edge portion of said recording head when said following image area is recorded, so that said total of ink quantity is obtained.   
     
     
       10. An ink-jet recording method as claimed in claim 9, wherein a number of ink droplets being landed on one pixel is controlled based on said density data. 
     
     
       11. An ink-jet recording method as claimed in claim 10, wherein a total number of ink droplets is a number of ink droplets being determined to obtain a predetermined tone wedge of a recording image of pixels when said pixels are formed without overlapping thereof. 
     
     
       12. An ink-jet recording method as claimed in claim 9, wherein said recording head comprises heating elements each of which produces thermal energy for discharging said ink in response to an electric current. 
     
     
       13. An ink-jet recording method as claimed in claim 9, further comprising the step of adjusting a discharge position of said recording head relative to said recording medium for each recording step so that each pixel included in said overlapping portion is formed by partially overlapping one image portion being formed by a group of ink droplets discharged when said one image area is recorded and following image portion being formed by a group of ink droplets discharged when said following image area is recorded, by less than a pixel pitch. 
     
     
       14. An ink-jet recording method as claimed in claim 13, wherein said adjusting step comprises adjusting an amount of sub-scanning. 
     
     
       15. An ink-jet recording method as claimed in claim 13, wherein said adjusting step comprises adjusting a record starting position of said main-scanning. 
     
     
       16. An ink-jet recording method as claimed in claim 9, wherein said total of ink quantity is density data being determined to obtain a predetermined tone wedge of the recording image of pixels when said pixels are formed without overlapping thereof.